The Global Navigation Satellite System (GNSS), of which one component is the Global Positioning System (GPS), is a satellite-based navigation system. GNSS permits land, sea, and airborne users to determine their three-dimensional positions, velocities, and time. GPS uses NAVSTAR (NAVigation Satellite Timing and Ranging) satellites. The current satellite constellation consists of 21 operational satellites and 3 active spares. This constellation provides a GNSS device to receive signals from four to twelve GNSS satellites at any given time. A minimum of four GNSS satellites allows the GNSS device to compute its position (latitude, longitude, and altitude) and GNSS system time. Altitude is typically referenced to mean sea level. The GNSS satellite signal from the GNSS satellites contains information used to identify the GNSS satellite, as well as to provide position, timing, ranging data, satellite status, and the updated ephemeris (orbital parameters). Coarse orbital information is available in the almanac data. The ephemeris data contains higher accuracy orbital position information.
Satellite signal acquisition requires a relatively long period of time, particularly during a cold start initialization of the GNSS device (the GNSS device has no current location information for itself and/or for any satellites, and/or the GNSS device does not know time). During warm start initialization, the GNSS device does have some information, such as relatively recent almanac data and/or ephemeris data, and/or an estimate of time that may be used to speed up the GNSS satellite signal acquisition process. However, the time to acquire a GNSS satellite signal for one GNSS satellite, and the total time required to acquire four or more GNSS satellite signals, is very noticeable to the user of the GNSS device. That is, the user of the GNSS device has to wait for some discernable period of time until position information is presented. Accordingly, it is desirable to reduce the GNSS satellite signal acquisition times.